1. Field of the Invention
This invention relates to a welding apparatus.
2. Description of the Related Art
Conventionally, as shown in FIG. 7 and FIG. 8, a welding apparatus, provided with an electrode die portion c having a lower base portion a and an upper base portion b elevatable as to close to and part from the lower base portion a, plural lower electrode portions d arranged on the lower base portion a, plural upper electrode portions e arranged on the upper base portion b, and an elevation driving mechanism which ascends and descends the upper base portion b, is known.
To explain in further detail, the upper electrode portion e has welding electrode pressurizing cylinder guns g supplied with cooling water circulation in unpressurized state and pressed to contact a welded object f placed on the lower electrode portions d in pressurized state, and each of the cylinder guns g is connected to a cooling water circulation supplying duct h. And, a booster i is disposed on an upstream side to the cylinder guns g in the duct h, and a stop valve j is disposed on a downstream side to the cylinder guns g in the duct h. In FIG. 7 and FIG. 8, plural cylinder guns g form a group, and one booster i and one stop valve j are provided as to correspond to the group. That is to say, this welding apparatus is provided with plural boosters i and stop valves j respectively corresponding to the groups of the cylinder guns g.
FIG. 8A shows unpressurized state of the cylinder gun g. Both of the booster i and the stop valve i are in open state, and cooling water is circulated and supplied to the cylinder gun g through the duct h. In welding, as shown in FIG. 8B, the stop valve i is closed by supplying compressed air with switching an electromagnetic valve k, the booster i is worked to become closed state by supplying compressed air with switching an electromagnetic valve m, and the cylinder guns g of one group are extended by pressurizing the cooling water in the duct h from the booster i to the stop valve i through the cylinder gun g to contact and weld the welded object f placed on the lower electrode portions d. And, in FIG. 8B, biased portion represents the pressurized cooling water.
However, there are problems that each of the boosters i and the stop valves j, used once or twice in one cycle of production, require large installation space for their utilization rate, and, the electromagnetic valves k and m, corresponding to each of the boosters i and the stop valves j, cause high cost.
And recently, for example, for changes in crash safety standards of automobiles, number of pressed parts and welding spots have been inclining to extremely increase along with increasing rigidity of automobile body, upper and lower electrode portions in one welding apparatus have been increasing thereby, and increase of number of parts such as a booster and structural complication of the apparatus have been generated. Further, there is a problem directly relating to weldability that pressure control of many (eighteen, for example) boosters can not be set individually in one cycle of production in conventional gun pressurizing control, and a welding element, namely, pressurizing control is forced to be constant.
And, concerning the elevation driving mechanism which ascends and descends the upper electrode portions, many parts cause much cost for that a crank elevation driving mechanism is used as the elevation driving mechanism, and it has bad influence on operating rate of production that die height (the height of the die) is manually set and the die is changed semi-automatically.
To solve the problems above, it is therefore an object of the present invention to provide a welding apparatus with which constructural simplification and reduction of production cost can be achieved, and multi-point welding can be conducted with high accuracy.